In order to reduce the amount of energy needed for polymerizing vinyl monomers and for evaporating and burning solvents they are in, various types of radiation cures have been tried. Ionizing radiation, such as X-rays, randomly knocks off atoms and groups producing a highly cross-linked polymer. However, because ionizing radiation is difficult to handle safely, it has not been widely used.
Ultraviolet radiation has also been used in combination with a photo-initiator which initiates the polymerization; but because of the absorption characteristics of materials, the light can only penetrate to a depth of about 20 mils. When the monomer is pigmented or opaque materials are present in the resin, the depth of cure is even less.